Plate feeding apparatus

ABSTRACT

Plate feeding apparatus for feeding plates from a plate stack is described. The apparatus comprises a deflectable separator and a feed member. In use, the feed member is adapted to urge the endmost plate in the stack against the separator, thereby causing deflection of the separator so as to allow no plates other than the endmost plate to be fed to a position downstream of the separator.

FIELD OF INVENTION

This invention is directed to apparatus for reliably feeding a single printing plate and interleaf paper from a stack of media. In particular, the invention is directed to accurately and straightforwardly delivering a single plate from a cassette of plates to an image setter or other machine in an imaging process.

DESCRIPTION OF RELATED ART

Printing plates are normally supplied in a stack with an interleaf paper between each plate to ensure that one plate does not scratch another. In many situations, it is necessary to automatically feed the plates one by one into a system or machine. For example, a computer to plate image setter machine is typically provided with printing plates from a cassette, the cassette holding a stack of plates with an interleaf paper between each one. The interleaf paper may not always be present, for example when two batches of media are loaded into a single cassette, the top of the first and bottom of the second batch will have no interleaf. The plate feeding means must be able to reliably remove a plate from the stack, feed it into the imaging engine or other machine and discard the interleaf sheet (if present). It is particularly important that a single printing plate and associated interleaf paper are removed from the cassette in each turn. Multiple plate feeding can lead to jams in the plate transport system and wastes printing plates. Furthermore, if a plate is partially fed out of the cassette, when the cassette needs to be replaced, the partially fed plate must be reversed back into the cassette before the cassette can be changed. This is unreliable, difficult to achieve and slows the cassette change. If the plate is not fully reversed, it can cause jamming and effect the light-tightness of the cassette, wasting plates.

A conventional method for delivering a single plate and interleaf from a cassette is shown schematically in FIG. 1. A plate stack 12 is positioned adjacent to feed roller 10. A fixed metal lead edge guide or separator 11 is used to prevent more than one plate from leaving the cassette under the action of feed roller 10. The uppermost plate 5 and its associated interleaf paper 16 are urged out of the cassette, passing over separator 11.

The separator 11 is intended to prevent more than one plate with interleaf paper from leaving the cassette. This requires a plate stack lift system (not shown) capable of positioning the plate stack 12 accurately with the uppermost plate 5 above the top of the separator 11. In other words, the top of the stack must be positioned greater than one and less than two plate thicknesses above the top of separator 11. In practice, this is very difficult to achieve accurately as the minimum plate thickness is typically 0.15 millimetres and there may be a variation in height due to the stack lift mechanism and height sensing method. This means that this conventional mechanism is not accurate enough to give reliable feeding between a full and nearly empty cassette, and that in practice more that one plate (and interleaf) may pass over separator 11.

The plate(s) fed over separator 11 are transported downstream to an interleaf separator comprising a second feed roller 13 and friction retard system 14. This has to both ensure that only a single plate travels any further downstream and that the plate 5 is separated from the interleaf sheet 16. This is achieved by feeding only a single piece of media (plate 5 or interleaf sheet 16) at a time, delivering the plate 5 forward to the imaging engine whilst discarding the interleaf paper 16. This technique is slow but is necessary to cope with multiple plate feeds from the cassette.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention, plate feeding apparatus for feeding plates from a plate stack is provided, comprising:

-   -   a deflectable separator; and     -   a feed member; wherein in use the feed member is adapted to urge         the endmost plate in the stack against the separator, thereby         causing deflection of the separator so as to allow no plates         other than the endmost plate to be fed to a position downstream         of the separator.

The use of a deflectable separator (also known as a “flexible lead edge guide”) which can be deflected by a plate, does away with the need for accurate alignment of the separator with the top of the plate stack. The apparatus reliably allows only a single plate to be fed at a time, thus avoiding problems such as jamming caused by multiple plate feeding. Further, since only one plate exits the cassette at a time, no plates are partially fed out and cassettes may be changed faster and more reliably. The term “deflectable” includes both the separator moving as a whole, rotating for example, and the separator being deformed itself, bending for example. Movement of the endmost plate deflects the separator and as its angle increases, the plate moves to the top of the separator and is then able to move over it.

The use of a deflectable separator also means that the plate stack does not need to be accurately positioned relative to the separator. The angle of the plate stack can be varied without the stack or the deflectable separator needing to be adjusted. Similarly, different thicknesses of plate can be separated without having to adjust the stack height or separator.

This apparatus also enables the overall media handling time to be reduced. By reliably feeding only a single plate (and interleaf, if present), it is possible to use a faster interleaf separating device downstream than in the conventional method. In particular, the interleaf separating device does not need to be able to cope with multiple plate feeds.

Preferably, the apparatus further comprises a plate support for holding the plate stack against the feed member. Typically, the plate support is moveable towards the feed member so as to enable the endmost plate to contact the feed member. This may be achieved using a lift system comprising, for example, a stepper motor or spring. However, the plate support could be fixed and the feed member moveable instead.

Preferably the feed member comprises a feed roller although other feeding means may be employed, such as friction belts.

The separator is typically positioned adjacent to the plate support although the separator could be an integral part of the plate support. The separator could be coupled to the plate support by means of a hinge or pivot point for example.

Preferably, the separator is movable between a plate retention position to retain the passage of the plate and a deflected position which allows the passage of the plate to the downstream position. Typically, the separator is biassed towards the plate retention position, possibly by means of a spring or the use of a resilient material. Generally the separator is one or more of a panel, flap or tab. The separator may be rotatable about an axis and could, additional or alternatively, itself be deformable.

Preferably, the plate feeding apparatus further comprises an interleaf separator, downstream of the separator and operable in use to separate any interleaf sheets from the endmost plate when they have passed the separator together.

In accordance with a second aspect of the invention, an image setter is provided which comprises plate feeding apparatus in accordance with the above-described first aspect of the invention. However, the plate feeding apparatus according to the first aspect of the invention could be used to automatically feed plates to other types of machine. The plates fed by the apparatus could also include other types of sheet media such as films or cards having sufficient stiffness to cause the separator to deflect.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of this invention will now be described in detail with reference to the following figures, wherein:

FIG. 1 shows a conventional plate feeding system;

FIG. 2 shows an example of a plate feeding apparatus before feeding of a plate;

FIG. 3 shows the plate feeding apparatus of FIG. 2 in which the endmost plate is moved;

FIG. 4 shows the plate feeding apparatus of FIGS. 2 and 3 as the endmost plate exits the cassette;

FIG. 5 schematically shows the main components of an image processing system; and

FIG. 6 is a schematic end view of a conventional image setter.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the image processing system schematically shown in FIG. 5, an original image 1 (such as a continuous tone colour print or transparency) is scanned by an input scanner 2 which generates a set of grayscale image files 3. The image files 3 are input to an image setter 4 which converts the grayscale image files 3 into bitmap form and forms prints a set of film separations on plates 5 in accordance with the calculated bitmaps. The plates 5 are then mounted on a film processor 6 which generates a set of printing plates 7. The printing plates 7 are then mounted on a printer 8 which produces a colour print 9.

A conventional image setter 4 is shown in detail in FIG. 6. A plate 5 is fed into the image setter from a cassette (not shown). The image setter comprises a drum 50 with a semi-cylindrical internal profiling surface 51. The plate 5 is mounted on the surface 51 by attaching one end of the plate 5 to a loading carriage 53 which traverses round the drum. After the plate 5 has been loaded, it is exposed by a scanning radiation beam 54.

Plate feeding apparatus for feeding each plate from the cassette into the drum is shown in FIG. 2. The plate 5 is the uppermost plate on plate stack 12. Interleaf sheets are not shown for clarity, but, if present, they would lie between each plate in the plate stack 12. It should be noted that whilst the Figures show the plate stack 12 in a horizontal position it would also be possible to orientate the cassette differently, in which case the plate 5 may not be described as the uppermost but regardless of the orientation, it will be the endmost plate.

The plate stack 12 is supported on plate support 21 which is provided with a lift system (not shown) to move the plate stack 12 up and down (direction A in FIG. 2). The plate support 21 is typically supported on a base 23 which is fixed. A deflectable separator 20 is provided at one end of base 23. Typically, the separator 20 is fixed relative to the base 23 (in the A direction) and the plate support 21 is movable but this could be arranged in the opposite sense.

In the example shown, separator 20 consists of a rigid panel of material attached to the base 23 by means of a spring 22, but it could be a separate component. Alternatively, separator 20 could be an integral part of base 23 or plate support 21 and could itself be deformable, for example it could be made from a resilient material. The separator can be deflected or pivoted between a plate detection position (shown in solid lines) which prevents plates exiting the cassette, and a deflected position (shown in dashed lines) which allows the passage of a plate to a position downstream, and usually into a machine such as image setter 4.

A feed roller 10 is provided which contacts the endmost plate 5. When the plate 5 is to be fed out of the cassette, the feed roller 10 turns and urges the plate 5 towards separator 20. When plate 5 contacts the separator, the separator is deflected in the direction C. As the angle of the separator 20 increases, the plate 5 starts to move to the top of the separator 20. When the edge of plate 5 is above the top of the separator 20, it is able to move forward in downstream direction B while any other plates in the plate stack 12, which were carried forward with the plate stack 5, are prevented from moving by the separator 20.

This is achieved because the separator 20 has a range of heights where if enough force is applied, the plate can pass over the separator 20. With the feed roller only in contact with the endmost plate, only the endmost plate has enough force applied to it to deflect the separator 10. This is because the friction between one plate and the plate below is less than the friction between the feed roller 10 and the endmost plate 5 so only the endmost plate 5 is driven forward with sufficient force. The maximum angle of the separator 20 is controlled by the driving force applied and the spring rate for the particular spring 22 (or resilient material) used. Since the separator 20 can deflect in response to a force applied over a range of positions (in the A direction), it is no longer necessary to accurately align the plate stack 12 with the separator 20.

If an interleaf sheet is present, it is moved with the plate above it by the feed roller 10. This is because the interleaf paper generally has a lower friction against the top surface of the plates (which typically may be coated) than the lower surface (typically uncoated). The plate 5 and interleaf may then be transported to an interleaf separator downstream. This could comprise a second feed roller and friction retard system as used in the conventional apparatus shown in FIG. 1 where the plate 5 and interleaf 16 are separated and fed out separately. Alternatively, a device (not shown) which simultaneously feeds the plate, removes the interleaf and stores it in a paper bin could be used. This technique is faster and would reduce the overall media handling time.

The separator 20 may be in the form of one or more deflecting panels, tabs or flaps. A typical separator 20 consists of a piece of material such as Delrin™, which is a polymer with good durability and which does not scratch the printing plates. Other materials such as Mylar™ and PET could alternatively be used but they have been found to be less durable and to have sharp edges which could damage the plates. Typically such a panel or tab would be biassed by a spring or other resilient component. In such an arrangement, the separator 20 may pivot or rotate about an axis when deflected by the oncoming plate 5 from a plate retention position (shown in solid lines in FIG. 2) to a deflective position (shown in dashed lines in FIG. 2), returning to the plate retention position once the plate 5 has passed.

Alternatively, the separator could be formed from a resilient material such a foam or rubber which, rather than moving as a whole as shown in the diagrams, could, on contact with the plate 5, resiliently bend or flex. This would cause the plate 5 to move to the top of the separator 20 in the same way as described above. With this arrangement, a spring or other biassing means may be unnecessary. The separator 20 could for example be a fin of rubber, wider at the base and thinner at the top so as to achieve the desired deflection.

The use of a deflectable separator 20 means that the plate stack 12 does not have to be accurately aligned with the top of the separator because the selection of the endmost plate is dependent on the movement of the separator 20 rather than the particular position of the plate. Similarly, the apparatus can feed different thicknesses of plates without needing the adjust the stack height or separator deflection.

The apparatus is also convenient because the plate stack 12 does not have to be accurately positioned parallel to the separator 20 and thus the angle of the plate 12 can be varied, again without needing to adjust the stack height or separator deflection. 

1. Plate feeding apparatus for feeding plates from a plate stack, comprising: a deflectable separator; and a feed member; wherein in use the feed member is adapted to urge the endmost plate in the stack against the separator, thereby causing deflection of the separator so as to allow no plates other than the endmost plate to be fed to a position downstream of the separator.
 2. Plate feeding apparatus according to claim 1 further comprising a plate support for holding the plate stack against the feed member.
 3. Plate feeding apparatus according to claim 2 wherein the plate support is movable towards the feed member so as to enable the endmost plate to contact the feed member.
 4. Plate feeding apparatus according to claim 1 wherein the feed member comprises a feed roller.
 5. Plate feeding apparatus according to claim 2, wherein the separator is positioned adjacent to the plate support.
 6. Plate feeding apparatus according to claim 2, wherein the separator is an integral part of the plate support.
 7. Plate feeding apparatus according to claim 1 wherein the separator is movable between a plate retention position to retain the passage of the plate and a deflected position which allows the passage of the plate past the separator to the downstream position.
 8. Plate feeding apparatus according to claim 7 wherein the separator is biassed towards the plate retention position.
 9. Plate feeding apparatus according to claim 8 wherein the separator is biassed towards the plate retention position by a spring.
 10. Plate feeding apparatus according to claim 1 wherein the separator is one or more of a panel, flap or tab.
 11. Plate feeding apparatus according to claim 1 wherein the separator is rotatable about an axis.
 12. Plate feeding apparatus according to claim 1 further comprising an interleaf separator, downstream of the separator, and operable in use to separate any interleaf sheets from the endmost plate when they have passed the is separator together.
 13. An image setter system comprising plate feeding apparatus according to claim 1 and an image setter to which plates are supplied by the plate feeding apparatus. 